The extent of prophylactic lateral neck lymph node dissection is very controversial in medullary thyroid cancer. This retrospective study was undertaken to evaluate the efficacy of prophylactic lateral neck lymph node dissection.

A total of 29 patients underwent curative operation for medullary thyroid carcinoma at our institution. Of these 29 patients, 13 patients had prophylactic lateral neck dissection and 16 patients had non-prophylactic lateral neck dissection. Among 13 patients, one-compartment prophylactic lymph node dissection was performed in 10 patients and two-compartment prophylactic lymph node dissection was performed in 3 patients. Postoperative calcitonin level was evaluated between these groups.

A normalized calcitonin level was detected after surgery in 74% of patients without lateral neck lymph node metastases, and in 10% of patients with lateral neck lymph node metastases. In comparison of prophylactic node dissection group and non-prophylactic node dissection group, the rate of normalized calcitonin level after surgery is 100%, 66.7% in stage 1, 100%, 50% in stage 2, 0%, 80% in stage 3, 14.3%, 0% in stage 4. In the patients who one-compartment prophylactic lymph node dissection was performed, 40% of patients had positive lymph node metastasis, and 70% had persistent hypercalcitoninemia. However, there was no postoperative hypercalcitoninemia in the patients with twocompartment prophylactic lymph node dissection although lymph node metastasis was not identified with pathologic examination.

Prophylactic lymph node dissection was more effective in the early stage of medullary thyroid carcinoma than late stage. The two or more compartment lymph node dissection is more effective than just one-compartment dissection for the normalization of serum calcitonin level.